Method and apparatus of forming integral ribs on tubes



March 18, 1969 E. K. HENRIKSEN 3,433,039

METHOD AND APPARATUS OF FORMING INTEGRAL RIBS ON TUBES Filed Feb. 24. 1966 Sheet of INVENTOR.

ERIK'HE RIKSEN W7 yz ATTORNEYS March 18 1969 E. K. HENRIKSEN METHOD AND APPARATUS OF FORMING INTEGRAL RIBS 0N TUBES Z of 2 Sheet Filed Feb. 24, 1966 S R v E m H N NS R E O VR mu /W H uh K m E Y 78 Q G F United States Patent 3,433,039 METHOD AND APPARATUS 0F FORMING INTEGRAL RIBS 0N TUBES Erik K. Henriksen, Downey, Calif., assignor to Aerojet- General Corporation, El Monte, Calif., a corporation of Ohio Filed Feb. 24, 1966, Ser. No. 529,880

US. Cl. 72-56 Claims Int. Cl. B21d 26/02, 22/10; B213 5/04 ABSTRACT OF THE DISCLGSURE This disclosure concerns a method and apparatus for forming integral longitudinally extending ribs on a tubular member by utilizing the energy generated from the detonation of explosive charges as a forming medium. The method employs two explosive forming sequences, each of which is carried on with a mandrel differing from the mandrel used in the other explosive forming sequence.

The first explosive forming sequence employs a first mandrel having an outer surface comprising alternating radially outwardly extending large radii portions of arcuate extent and small radii forming ridges. The first mandrel is inserted within the tubular member, and explosive charges located externally of the tubular member are detonated, thereby conforming the tubular member to the shape of the outer surface of the first mandrel. The second man drel which is cylindrical is then inserted within the tubular member for the second explosive forming sequence. The tubular member with the second mandrel inserted there- Within is received within a confining wall enclosure which includes a plurality of internal limit stops corresponding to the respective small radii ridges on the tubular member and in radially spaced relation thereto. Upon detonatmember, the large radii portions previously formed on the tubular member are forced against the second mandrel which has the effect of compressing the small radii ridges into ribs. The radial extent of the ribs as so formed is gaged by the limit stops.

The present invention relates generally to the forming of tubular workpieces with integral ribs, and, more particularly, to the forming of integral ribs on such tubes by the use of explosive techniques.

It is a not infrequent requirement that a tubular article be formed as to have longitudinally extending ribs and with outer and inner dimensions of a precise predetermined character. One usually employed technique is to take a cylindrical tube and form it against a suitable die or mandrel in order to provide the desired surface configuration. However, it has been found that when using a die that surrounds the tube, pressing of the tube into the die provides outer dimensions of a closely controlled character, but the inner dimensions do not neces sarily meet any prescribed standards. Again, if the tube is formed about amandrel of desired shape, the inner dimensions are found to be satisfactory, but the outer dimensions are not maintained to any particular prescribed standard.

It is therefore a primary purpose and function of the present invention to provide a method and apparatus for making a ribbed tube-like structure that will have both internal and external dimensions within precise tolerances.

It is another object of this invention to provide a method and apparatus for forming ribbed tube-like structures by the utilization of explosive forming techniques.

Still another object of the invention is to provide a method and apparatus for forming a special cylindrical tube having longitudinally extending rib portions, whereing explosive charges located externally of the tubular 'ice in the outer and inner dimensions of the tube are maintained within predetermined limits of tolerance.

Still further objects and features of the invention will hereafter appear from the following description when read with reference to the accompanying drawings illustrative of the invention.

In the drawings:

FIG. 1 is a fragmentary transverse sectional view of the apparatus of the invention before initiating operation.

FIG. 2 is a fragmentary transverse sectional view of the apparatus of FIG. 1 illustrating completion of the first step of the method of the invention.

FIG. 3 is a fragmentary transverse sectional view similar to that of FIGS. 1 and 2 after completion of the second step of the invention with integral ribs formed on the workpiece.

FIGS. 4-6 show respective fragmentary elevational views of several stages of formation of integral ribs during practice of the method of the invention.

FIG. 7 is a fragmentary longitudinal sectional view taken along the line 7-7 of FIG. 2 and drawn to a smaller scale.

FIGS. 13 only illustrate a transverse sectional view of approximately one-fourth of the entire apparatus, anc it is to be understood that the remaining three-fourths is identical in construction. Similarly, FIG. 7 shows a longitudinal sectional view of only one portion of the apparatus, it being understood that the entire apparatus actually consists of a generally cylindrical construction.

With reference now to FIGS. 1-3 and 7, one form of apparatus for practicing the method of the invention is seen to include generally a base plate 10 disposed in substantially horizontal condition. Mounted onto the upper surface of the base plate is an upstanding substantially cylindrical wall 11, the wall portions of which are formed into a plurality of longitudinally extending inner chambers 12 separated by inwardly directed protrusions 13. The upstanding wall 11 is constructed of a material of sufiicient rigidity and strength to withstand the explosive detonation forces without deforming. Via flanges 14 (FIG. 7), the wall 11 is secured to the base plate 10 and to a cover 15 through the instrumentality of conventional threaded members 16.

Concentrically arranged within the upstanding wall is an open-ended cylindrical positioning sleeve 17 that is received at its lower end within appropriately dimensioned grooves in the upper surface of the base plate 10. The plate and sleeve are secured together by threaded members 18. At its supper end, the positioning sleeve is likewise received within an appropriately shaped groove in the cover 15. A first forming mandrel or die 19 is a generally cylindrical construction and adapted to be received over the positioning sleeve 17 in a tight fitting relation. To prevent twisting or turning of the first forming member during explosive forming, a key 20 on the inner surface of the member is received in a similarly dimensioned groove on the outer surface of the positioning sleeve. The first forming member is provided with a plurality of small radii forming ridges 21 extending longitudinally throughout the complete length of the member. The ridges are so arranged as to lie directly opposite a corresponding inwardly directed protrusion 13, the coaction of which to achieve the adavntages of the invention will be set forth later herein. Intermediate the ridges 21 are relatively large radii portions 22, also extending radially outwardly of the forming member 19.

In utilizing the above-described apparatus to practice the first step of the invention, a tubular or cylindrical workpiece 23 is inserted downwardly Over and in concentric relation to the first forming member 19. The inner wallsurface of the workpiece is either in contact with or slightly spaced from the small radii forming ridges 21. Next, the cover is secured over the assembly by threaded members 16. Generall elongated rod-like explosive charges 24 are received within the chambers 12 (FIG. 7) and secured by suitable threaded inserts 25 and 26 within the base plate It) and cover 15, respectively. Initiators 27 operatively related to each of the explosive charges are initiated simultaneously via electrical wires 28 to detonate the charges. Detonation effects forming of the workpiece 23 onto and over the first forming member 19 as shown in FIG. 2. It is to be especially noted that after this first step of the method, the workpiece 23 includes a partial forming of the outer surface into intermediate ribs 21' matching the forming ridges 21, and more gently curved areas 22' corresponding to the portions 22. The cover 15 is now removed. Then, the first forming member 19 including the partially formed workpiece thereon is removed, and the workpiece is stripped off with care being taken not to deform the partially finished workpiece.

A final forming mandrel 29 of identical inner dimensions to member 19 is keyed onto the positioning sleeve 17. The outer surface of the mandrel is a smooth cylinder. The partially formed workpiece is placed on the mandrel assuming a position substantially as shown in the dashed line illustration in FIG. 3. That is, only the innermost surface of the workpiece 23 is in contact with the outermost surface of the mandrel. As before, the cover is secured in place, and further rod-like explosive charges are placed in position within the chambers 12 and detonated. Detonation this time serves to move the curved portions 22 into direct contact with the outer surface of the cylindrical mandrel 29 as shown in a solid line. Also, detonation serves to close up the curved portions 21' until the side walls are in substantially contacting relationship as shown in the solid line configuration. When the latter occurs, the radial extensions of the workpiece at the ribs 21' are gaged by the inwardly directed protrusions 13 of the upstanding wall 11 to the required height. Removal of the cover and stripping of the workpiece from the mandrel is all that remains to be done.

It is seen that the final formed workpiece includes the desired plurality of ribs running longitudinally along its outer cylindrical surface, each of the ribs being closely gaged to a predetermined value, whereas the inner dimensions are within a very close tolerance, the same as the external dimensions of the mandrel 29.

It is seen that the only dimensions which are predetermined by the required final shape of the workpiece are the diameter of the circle inscribed within and in contact with the inner-most points of the protrusions 13, and the outer diameter of the final forming mandrel 29. Within these limits, there is considerable freedom for the selection of the detailed dimensions of the outer configuration of the first forming mandrel 19, as well as for the selection of the diameter of the workpiece Z3, and it is therefore possible to select the geometry and dimensions of these elements such that they will accommodate a workpiece of such diameter, that its peripheral length is equal to, or nearly equal to, the circumferential length measured on the formed workpiece after the first forming operation as well as after the final forming operation. That is, these forming operations will essentially comprise bending alone, with little or no overall elongation.

If a slight elongation does result, it will be evenly distributed over the circumference of the tubular workpiece 23, due to the soft curves in the configuration of the surface of the first forming mandrel. Accordingly, the invention is particularly well suited for application to materials of low ductility or elongation capabilities.

FIGS. 4-6 show variations of integral ribs that are obtainable through practice of this invention. The differences are achieved by using different ratios of diameter of the workpiece to that of the mandrel 29, or different distances between the protrusions 13 and the ridges 21, for example.

While a particular embodiment of the invention has been illustrated and described, it will be understood that the invention should not be construed as being limited thereto, but only to the lawful scope of the appended claims.

I claim:

1. Method of forming integral ribs on a tubular workpiece, comprising: shaping the workpiece into a plurality of relatively small radii ridges separated by relatively large radii portions; and directing a force against the convex side of the large radii portions to shape them to lie along the same circumferential line of a single circle, thereby compressing the small radii ridges into the desired integral ribs.

2. Method of forming as in claim 1, in which the shaping step includes impressing the tubular workpiece onto a first mandrel to form the small radii ridges and large radii portions with their convex side disposed outwardly, supporting select portions of the inner wall surfaces of the tubular workpiece by a second mandrel while performing the step of directing the force against the convex side of the large radii portions such that the inner wall surfaces of the finished tubular workpiece will be in flush intimate contact with the second mandrel other than at those inner wall surface portions included in the formation of the integral ribs.

3. Method of forming as in claim 2, in which the shaping and force directing steps are respectively accomplished in sequence by simultaneously detonating a plurality of explosive charges disposed about the tubular workpiece.

4. Method of forming integral ribs on a tubular workpiece, comprising: shaping the tubular workpiece into a plurality of relatively small radii ridges separated by relatively large radii portions formed with their convex sides disposed outwardly by impressing the tubular workpiece onto a first mandrel; and supporting select portions of the inner wall surfaces of the tubular workpiece by a second mandrel, and locating a limit stop radially outwardly of each of the small radii ridges a predetermined distance, while directing a force against the convex side of the large radii portions to shape them to lie along respective arcuate portions having the same radius of curvature, thereby compressing the small radii ridges into the desired integral ribs, with the inner wall surfaces of the finished tubular workpiece being in flush intimate contact with the second mandrel other than those inner wall surface portions included in the formation of the integral ribs, and the maximum extent of the finished ribs being gaged by the location of the respective limit stops for each of the small radii ridges.

5. Apparatus for providing integral ribs on a tubular workpiece having a plurality of relatively small radii ridges on its outer surface, comprising: walls defining a closed chamber; a mandrel disposed within the chamber for receiving the tubular workpiece thereabout, the relative dimensions being such that the major inner surface areas of the tubular workpiece are spaced from opposing surfaces of the mandrel; explosive charge means located within the chamber and externally of the tubular workpiece such that detonation of said explosive charge means serves to form the tubular workpiece onto the mandrel; and stop limit means disposed within the chamber and spaced directly opposite the small radii ridges of the tubular workpiece a predetermined distance, whereby upon detonation of the explosive charge means, forming of the major inner surface areas of the tubular workpiece onto the mandrel caused by the energy generated from the detonation of the explosive charge means folds the ridge walls of each respective small radii ridge onto each other causing the so-shaped ribs to extend radially outwardly into contacting relationship with the stop limit means corresponding thereto.

6. Apparatus as in claim 5, in which the stop limit means are integral with the walls defining the chamber.

7. Apparatus as in claim 6, in which the walls of the chamber include side walls having alternating inwardly projecting surfaces and wells therebetween, the explosive charge means being individually located in the wells and the inwardly projecting surfaces acting as the stop limit means.

8. Apparatus as in claim 5, in which the walls defining the closer chamber include side walls, a base plate to which the side walls are secured, a removable cover closing the top of the chamber, said base plate and said cover having aligned grooves formed therein, and the mandrel being received within said grooves formed in the base plate and cover positioning it throughout operation.

9. Apparatus as in claim 8, in which the explosive charge means includes a plurality of rod-like charges having their ends received in the cover and base plate, respectively, and being arranged in uniform surrounding relationship to the tubular workpiece and mandrel.

10. Apparatus as in claim 5, in which the mandrel dimensions and spacing of the stop limit means are such relative to the dimensions of the tubular workpiece, that forming of the workpiece to its final shape is achieved with substantially no elongation of the workpiece as measured in the general plane of the workpiece material, thereby permitting use of the apparatus with workpiece materials of relatively low ductility or elongation capabilities.

References Cited UNITED STATES PATENTS 1,378,442 5/1921 Chalfant 72-60 3,173,196 3/1965 Grimm 72367 3,287,947 11/1966 Frantz 7256 CHARLES W. LANHAM, Primary Examiner.

K. C. DECKER, Assistant Examiner.

US. Cl. X.R. 7260, 370; 315194, 251; 323-24, 36 

